Intermittent Brake Drag Or Brake Aggressive - keywords 5A C0131 C0135A pad pedal pulsation rotor wheel wear

This PI was updated to add Avalanche and EXT. Please discard PIT4081A

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some customer may report their vehicle has an intermittent brake drag; brakes are getting hot or aggressive. This concern may be also followed by a DTC C0131 symptom code 5A set in the EBCM. This concern may be caused by a brake booster or a master cylinder concern. Please use the following diagnosis for assistance on finding a brake booster or master cylinder concern.

If the Dealer investigation confirms brake drag symptoms on all 4 wheels, please use the following diagnostic procedure:

Note: This procedure should only need to be performed on vehicles built before 05/03/06

Diagnostic Procedure

1. Lightly pull up on brake pedal (5 lbs. of force or less). NOTE: Excessive force can damage the vacuum booster.
2. Start vehicle (assure adequate ventilation) and leave vehicle transmission selector in Park.
3. Make a light apply to the brake pedal (roughly 10 lbs. of force) and release slowly.
4. Lightly pull up on the brake pedal (5 lbs. of force or less). Note approximate distance traveled.
5. Make a hard brake apply (roughly 50 lbs. of pedal force) and release slowly.
6. Pull up on the brake pedal (5 lbs. of force or less). Note approximate distance traveled
7. If the travel noted when pulling up on the pedal in step #6 is noticeably greater than that in step #4, repeat the procedure a second time to verify measurements.
8. If the increased travel noted in step #6 is confirmed a second time, the brake booster should be replaced.

If the Dealer investigation confirms brake drag symptoms on EITHER front OR rear brakes, but NOT BOTH, please use the following diagnostic procedure:

Note: This procedure should only need to be performed on vehicles built before 04/12/06

Diagnostic Procedure

1. Complete only after the vacuum booster drag test has been completed.
2. Drive the vehicle for 15 minutes or until signs of brake drag are noticed.
3. Return to the dealership and immediately raise the vehicle on a hoist (follow proper safety procedures).
4. Turn each of the four wheels by hand.
5. If either both front OR both rear wheels cannot be turned or have excessive drag, the brake master cylinder may be the cause. If all 4 wheels have excessive drag, retest for vacuum booster issue.
6. To verify the master cylinder is the root cause, momentarily crack open the lines at the master cylinder. If the wheel immediately becomes easier to turn, replace the master cylinder.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.